Ims enabled attach procedure for lte

ABSTRACT

Method and apparatus for attaching an IMS enabled wireless transmit/receive unit (WTRU) to a long term evolution (LTE) wireless network. With one attach request, the WTRU registers and authenticates itself to the network, obtains an IP address allocation, and SIP registration.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. Provisional Patent Applications No. 60/735,442, filed Nov. 12, 2005 and No. 60/825,677, filed Sep. 14, 2006, which are incorporated by reference as if fully set forth.

FIELD OF THE INVENTION

This invention relates to a procedure for an Internet Multimedia System (IMS) enabled wireless transmit/receive unit (WTRU) to register itself to access and core networks and to the 3GPP Long Term Evolution (LTE) Enhanced UTRAN (EUTRAN), Enhanced Core (E-Core) Network and the IMS network system (IMS) and to obtain WTRU authentication, IP address allocation and Session Initiation Protocol (SIP) registration, and more particularly, to accomplish this in an efficient one-step ATTACH operation.

With the procedure set forth herein, the WTRU is able to achieve the ability to receive immediate incoming IMS calls and to perform faster outgoing call setup with the IMS network.

BACKGROUND

Hereafter, a wireless transmit/receive unit (WTRU) includes but is not limited to a user equipment (UE), mobile station, fixed or mobile subscriber unit, pager, or any other type of device capable of operating in a wireless environment. When referred to hereafter, a base station includes but is not limited to a Node-B, site controller, access point or any other type of interfacing device in a wireless environment.

The 3GPP has lately initiated the Long Term Evolution (LTE) program to bring new technology, new network architecture and configuration and new applications and services to the wireless cellular network in order to provide improved spectral efficiency, reduced latency, faster user experiences and richer applications and services at less cost.

With the advances of both wireless technology and internet technology, the integration of these two technologies and applications are the focus of the telecom industry. Given that the Internet Multimedia System (IMS) has already been specified, designed and implemented, tighter integration of the IMS into the current 3GPP and the future LTE takes on even greater importance. It is foreseeable that in the LTE network, WTRUs will be equipped with the IMS software and hardware and need to be a part of the system normal operation, including system initiation and registration.

It has been proposed for the LTE project that to reduce end-user latency, user and control plane separation in the Radio Access Network (RAN) should be implemented to optimize routing of user-plane and control-plane data. Similar concepts are applicable to Evolved High Speed Packet Access (HSPA) systems.

In current wireless telecommunication systems, when a WTRU switches on from the power-off state and gets camped with a cell, the WTRU will register itself to the network to obtain the subscribed services. This step is usually referred to as the ATTACH procedure, where the WTRU gets authenticated by the network and the network is updated as to where the WTRU is located. Subsequently, the WTRU is able to invoke outgoing calls and receive incoming calls via paging. Recently, this ATTACH procedure is even able to obtain an IP address for the mobile device, whereby direct dialog with another internet device is made possible by the extended ATTACH procedure.

However, this extended ATTACH procedure has not provided help for the prevailing IMS service, For any IMS enabled mobile device, additional steps/procedures beyond the ATTACH procedure are still required to make the mobile device IMS serviceable. As will be set forth below in the description of FIG. 1A, there is no provision for SIP Registration, which has to be performed after, and independently of, the extended ATTACH procedure, thereby preventing immediate use of the IMS service by the WTRU.

Without the SIP registration, the mobile device is further unable to receive incoming IMS (VoIP) calls and cannot set up any outgoing calls until the SIP Registration and IMS authentication is successfully completed.

Currently there is no specified approach for performing SIP Registration in synchronism with the completion of the ATTACH procedure, the result being that SIP Registration and subsequent IMS authentication are neither immediately nor automatically performed after the ATTACH procedure.

The inability to make IMS service available upon power up is due to the separation of the WTRU ATTACH procedure, shown in FIG. 1A, from the WTRU IMS SIP Registration, shown in FIG. 1B. On the user equipment side, the IMS SIP Registration is not part of the initial ATTACH procedure to attach the WTRU to the network. Also, the SIP Registration, as per the current WTRU ATTACH procedure, must await completion of the ATTACH procedure. In addition, the SIP Registration is not specified to immediately follow completion of the ATTACH procedure.

Considering all of the above, the IMS service cannot be used immediately after the WTRU powers up and users may have longer waiting times before the IMS service is ready for use. The separation of the SIP Registration and the ATTACH procedure also increases the number of signaling messages traveling between the WTRU and the E-Core, adding unnecessary network traffic load, both over the air and on landlines.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B respectively show signaling diagrams of a WTRU ATTACH procedure and an SIP registration procedure.

FIGS. 2A and 2B, taken together in the manner shown in FIG. 2, shows a signaling diagram of an IMS enabled WTRU ATTACH procedure.

FIG. 3 is a flow diagram of a WTRU MM (Mobile Management)-IMS synchronization procedure.

FIG. 4 is a bit allocation chart for an enhanced ATTACH REQUEST message for IMS SIP registration.

FIG. 5 shows an encapsulated SIP message within a Type 4 Information Element (IE).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Although the features and elements of the present invention are described in the preferred embodiments in particular combinations, each feature or element can be used alone (without the other features and elements of the preferred embodiments) or in various combinations with or without other features and elements of the present invention.

This invention provides a one-step ATTACH procedure to the LTE network with a system approach such that, when the WTRU powers up and performs the WTRU registration with the ATTACH procedure, it also performs the mission for IMS SIP Registration. At the completion of the ATTACH procedure, the WTRU is authenticated, its IP address is allocated and the IMS service is enabled via the SIP Registration, which is performed with the ATTACH procedure.

SIP registration is carried out by the ATTACH procedure at about the same time that the Enhanced Core (E-Core) Network is performing the ATTACH ACCEPT step. Providing parallel steps save the time otherwise needed for a subsequent IMS SIP registration, and also enables the ATTACH procedure to complete service registration together with mobile device registration.

As can be seen from FIG. 1A, the Attach request step S1 is conveyed to the Evolved Packet Core 14 from WTRU 10 through the Evolved Radio Access Network (RAN) 12, including Access Point Name (APN), Quality of Service (QoS), Protocol Configuration Options (PCO), etc. At S2, security functions are then performed, employing the Home Subscriber Server (HSS) 16 to update the WTRU's location and obtain subscription data, at S2 a. Radio resources are set up between core 14 and WTRU 10, at S3, resulting in the Attach Accept, S4, which includes providing the IP address, Protocol Configuration Options (PCO) and the like; and finally Attach complete, at S5.

FIG. 1B shows the SIP registration procedure, the SIP Register being conveyed from WTRU 30 to E-Core 20, at step Sa, to the Proxy Call Session Control Function (P-CSCF) 22 at Sb and to the IMS server 24 at Sc. Registration and authentication is performed at Sd, and SIP Authorization Challenge is conveyed to P-CSCF 22 at Se, and WTRU 30 at Sf, which performs IMS Authentication and Key Agreement (AKA) and prepares the Authorization response at Sg. The SIP Register Authorization response is conveyed from WTRU 30 to P-CSCF 22 at Sh and then to IMS Server 24 at Sh. IMS Server 24 checks the Authorization response, completes the IMS authorization and registration at Si and conveys the SIP Authorization OK to P-CSCF 22 at Sj and to WTRU 30 at Sk, completing SIP registration. It can be seen that the procedures in FIGS. 1A and 1B are independent of one another and there is no automatic triggering of the SIP procedure from the Attach procedure.

FIG. 2 shows the system coordination for the enhanced one-step ATTACH procedure with SIP Registration. SIP registration is carried out by the ATACH at about the same time that the E-Core Network performs the ATTACH ACCEPT step. The following are the steps of the IMS Enabled ATTACH procedure as shown in FIG. 2.

The IMS capable WTRU 40, powers up at Sa′ and is camped on a cell, whereupon the WTRU 40 prepares for the registration to the network, at Sb′, which, at Sc′, includes the activation of the equipped network services the WTRU 40 subscribes to, IMS in particular. The IMS Stack component SIP also initiates the SIP Registration request to the WTRU Non-Access Stratum (NAS) 42. The WTRU NAS 42 conveys the ATTACH procedure at Sd′ as well as the SIP registration request if it is an IMS enabled WTRU, during the MM-IMS Initial Synchronization procedure shown in FIG. 3 and described below in detail.

The WTRU NAS ATTACH procedure, by way of WTRU Radio Resource Control (RRC) 44, constructs the ATTACH REQUEST message at Se′, which includes the SIP Registration information element, and formats the appropriate ATTACH Request Type (EUTRAN+IMS), to indicate to the network that this is an enhanced ATTACH REQUEST message that requests the E-Core 46 and the IMS Proxy server (P-CSCF) 50 and IMS Server 52 that SIP registration service be performed. The ATTACH REQUEST message, at Sf, is transported over the signaling link of the RRC Connection 44 by an RRC message (Initial Direct Transfer).

When E-Core 46 receives the enhanced ATTACH REQUEST message, E-Core 46, at Sg′, looks at the WTRU credentials in the message and performs the usual WTRU authentication with the HSS/AuC 48, which involves the exchange of AUTHENTICATION REQUEST and AUTHENTICATION RESPONSE messages between the WTRU and the E-Core 46 and security mode activation messages between the EUTRAN 45 and the WTRU 40, as shown at Sh′. At Si′ E-Core 46 further checks the request type and performs IP address allocation. For the enhanced ATTACH REQUEST attach type EUTRAN+IMS, the enhanced ATTACH procedure in E-Core 46, at Sj′, performs the Proxy Call Session Control Function (P-CSCF) address selection for selecting the IMS Proxy and, at Sk′ sends the ATTACH ACCEPT message to the WTRU NAS 42 of WTRU 40 with the chosen P-CSCF address, as well as the IP address and the P-TMSI. E-Core 46 and HSS/AuC 48 interface to update the WTRU location, IP address and contacts at Sl′. The ATTACH ACCEPT message also triggers the establishment of the user plane tunnels to the WTRU IMS with appropriate radio bearer support setup, at Sm′.

For the ATTACH REQUEST attach type EUTRAN+IMS, the enhanced E-Core 46 ATTACH procedure, at Sn′, sends to the chosen Proxy server 50 the “P-CSCF Initiate and SIP Registration Request” to start the SIP registration, the P-CSCF 50 forwarding the SIP Request to IMS server 52 at So′.

The SIP registration and its related actions for the particular IMS-enabled WTRU 40 are carried out among the HSS 48, P-CSCF 50 and the IMS server (I-CSCF and S-CSCF) 52, at Sp′. WTRU IMS authentication parameters and Authentication Vectors are retrieved from the HSS 48, one of them being selected to be sent to the WTRU IMS 40 for the Authentication Challenge via an SIP 4xx Auth-Challenge message, Sq′, to P-CSCF 50.

P-CSCF 50, at Sr′ sends the SIP 4xx Auth-Challenge message to WTRU IMS 40 via E-Core over an established user plane tunnel. Prior to this, the WTRU NAS 42 has received the ATTACH ACCEPT message, Sk′ from E-Core 46 which also forwards the P-CSCF address to the IMS stack. This P-CSCF address becomes the future destination of the SIP messages.

The WTRU IMS 40 receives the SIP 4xx Auth-Challenge message Sr′ and, at Ss′, performs the IMS authentication AKA (Authentication and Key Agreement) procedure, generating the security keys and the authentication response to the network. The SIP register authentication response St′ is sent via P-CSCF 50 to the IMS server 52 identified in the SIP Register Auth-Response message, at Su′.

The IMS server 52 (S-CSCF), at Sv′, checks the WTRU Authentication response and determines the authentication is a success (or a failure) and completes the registration of IMS-enabled WTRU 40 with HSS 48. IMS server 52 sends the SIP 2xx Auth-OK message Sw′ to P-CSCF 50, which sends the message to WTRU 40, at Sx′.

Receipt of the SIP 2xx Auth-OK message provides notice to WTRU 40 that both the SIP Registration and authentication are successful. The enhanced ATTACH procedure of the WTRU is completed, the IMS is registered and authenticated with the network and the WTRU is now ready for any incoming IMS/VoIP call and is further ready for any outgoing call setup as well.

FIG. 3 is a flowchart of Logical Procedures for a WTRU Mobile Management (MM)-IMS Initial Synchronization. The WTRU performs power-up, at Saa, and, at Sab, determining the MM to be detached and SM to be inactive, and, if UE IMS is enabled, branches to Sad, whereby the Mobility Management/GPRS Mobility Management (MM/GMM) entity, at Sad, queries the IMS service Hardware and Software (HW and SW) availability status and requests the IMS stack component (SIP) for its registration with the network.

The IMS/SIP entity, at Sae, obtains the relevant parameters from the USIM/ISIM to form a SIP Register Request message to the MM/GMM. When the MM/GMM receives the SIP Register request, it formats and sends the enhanced ATTACH REQUEST message to the network, at Saf, to register the WTRU and its IMS service at the same time. This enhanced ATTACH procedure ends with the reception of the ATTACH ACCEPT message, at Sag to place WTRU NAS in the MM-connected and SM-Active state.

Returning to step Sac, in the event that IMS is not enabled, the regular ATTACH procedure is initiated, at Sah, followed by reaction to the ATTACH ACCEPT as shown at Sag and described above.

Enhancements to the ATTACH REQUEST message are based on the following message content table shown in Table 1 and the terms are described according to 3GPP TS24.008, the Mobile radio interface Layer 3 (L3) specification, Core Network Protocols. TABLE 1 3GPP TS 24.008: ATTACH REQUEST message content IEI Information Element Type/Reference Presence Format Length Protocol discriminator Protocol discriminator 10.2 M V 1/2 Skip indicator Skip indicator 10.3.1 M V 1/2 Attach request message identity Message type 10.4 M V 1 MS network capability MS network capability 10.5.5.12 M LV 3-9 Attach type Attach type 10.5.5.2 M V 1/2 GPRS ciphering key sequence number Ciphering key sequence number 10.5.1.2 M V 1/2 DRX parameter DRX parameter 10.5.5.6 M V 2 P-TMSI or IMSI Mobile identity 10.5.1.4 M LV 6-9 Old routing area identification Routing area identification 10.5.5.15 M V 6 MS Radio Access capability MS Radio Access capability 10.5.5.12a M LV  6-52 19 Old P-TMSI signature P-TMSI signature 10.5.5.8 O TV 4 17 Requested READY timer value GPRS Timer 10.5.7.3 O TV 2 9- TMSI status TMSI status 10.5.5.4 O TV 1 33 PS LCS Capability PS LCS Capability 10.5.5.22 O TLV 3 ?? IMS SIP Registration IMS SIP Registration 10.5.xx.xx O TLV ? Abbreviations in Table 1 above relevant to the present invention are: M=mandatory; TV=type & value; TLV=type, length & value; IE=Information Element; IEI=Information Element Identifier. Other abbreviations include: Packet Switch Location Service Capability (PS LSC); Temporary Mobile Subscriber Identity (TMSI); International Mobile Subscriber Identity (IMSI); Discontinuous Reception (DRX).

The addition of the IMS SIP Registration IE enables the enhanced ATTACH REQUEST message to carry out the IMS SIP registration task as well as the typical functions of the ATTACH procedure.

FIG. 4 shows a bit allocation chart for a new ATTACH type EUTRAN+IMS or evolved HSPA+IMS which is provided herein for the enhanced ATTACH REQUEST to the LTE E-Core ATTACH procedure with IMS SIP Registration implied. This ATTACH type applies to the Combined ATTACH Request procedure as well.

The IMS SIP Registration IE may be either one of the following:

-   -   a. An encapsulated SIP Register message—This approach provides         the transparency of upper layer service protocol message to the         current MM entities, freeing the SIP rebuilding task of the         network element.     -   b. A condensed message element that is a minimum required for         the SIP Registration for a shorter ATTACH REQUEST message.     -   Table 2 shows the IMS SIP Registration IE provided as a Higher         Layer Signaling Message.

The Encapsulated SIP message as an IE is a Type-4 IE (per 24.007) as illustrated in FIG. 5. TABLE 2 IEI Information Element Type/Reference Presence Format Length XX IMS SIP Registration HigherLayerSignalingMessage M TLV 10.5.xx.xx

In FIG. 5, IEI is an ID (to be determined by 3G WG) indicating it is an encapsulated SIP message, LI is the length indicator for the value part and the value part contains the SIP message in full from the IMS stack.

The purpose of the IMS SIP Register IE information element is to provide IMS SIP registration together with the ATTACH REQUEST. This is an optional IE for those WTRUs that are equipped with IMS capability and are subscribers to the IMS service.

Table 3 below provides the proposed SIP Registration parameters based on the following specification: IETF RFC 3261, RFC 3261-SIP Session Initiation Protocol, IETF networking Group, June 2002.

The private and public user identities for IMS authentication IMS User Private Identity (IMPI) and IMS User Public Identity (IMPU) are according to the following 3GPP specifications:

-   -   3GPP TS 33.203, 3G Security; Access Security for IP-based         services, V6.8.0

3GPP TS 23.228, IP Multimedia Subsystem: Stage 2, V7.1.0. TABLE 3 IEI Information Element Type/Reference Presence Format Length Request-URI SIP-Request-URI 10.5.xx.xx M LV From SIP-From 10.5.xx.xx M LV To Sip-To 10.5.xx.xx M LV Call-Id SIP-Call-Id 10.5.xx.xx M LV Cseq SIP-Cseq 10.5.xx.xx M LV PrivateUserIdentity SIP-Register-IMPI 10.5.xx.xx M LV PublicUserIdentity SIP-Register-IMPU 10.5.xx.xx M LV XX Expire SIP-Expire 10.5.xx.xx O TV 5

A new, enhanced ATTACH ACCEPT message set forth herein brings the allocated IP address and the chosen P-CSCF address back to the WTRU. Table 4 below shows ATTACH ACCEPT message content. TABLE 4 3GPP TS 24.008: ATTACH ACCEPT message content IEI Information Element Type/Reference Presence Format Length Protocol discriminator Protocol discriminator 10.2 M V 1/2 Skip indicator Skip indicator 10.3.1 M V 1/2 Attach accept message identity Message type 10.4 M V 1 Attach result Attach result 10.5.5.1 M V 1/2 Force to standby Force to standby 10.5.5.7 M V 1/2 Periodic RA update timer GPRS Timer 10.5.7.3 M V 1 Radio priority for SMS Radio priority 10.5.7.2 M V 1/2 Radio priority for TOM8 Radio priority 2 10.5.7.5 M V 1/2 Routing area identification Routing area identification 10.5.5.15 M V 6 19 P-TMSI signature P-TMSI signature 10.5.5.8 O TV 4 17 Negotiated READY timer value GPRS Timer 10.5.7.3 O TV 2 18 Allocated P-TMSI Mobile identity 10.5.1.4 O TLV 7 23 MS identity Mobile identity 10.5.1.4 O TLV 7-10 25 GMM cause GMM cause 10.5.5.14 O TV 2 2A T3302 value GPRS Timer 2 10.5.7.4 O TLV 3 8C Cell Notification Cell Notification 10.5.5.21 O T 1 4A Equivalent PLMNs PLMN List 10.5.1.13 O TLV 5-47 B- Network feature support Network feature support 10.5.5.23 O TV 1 34 Emergency Number List Emergency Number List 10.5.3.13 O TLV 5-50 A- Requested MS Information Requested MS Information 10.5.5.25 O TV 1 Allocated PDP Address Packet Data Protocol Address 10.5.6.4 O lV 3-19 XX IMS Proxy Address P-CSCF Address or <Packet Data O ? ? Protocol Address> 10.5.xx.xx or <10.5.6.4>

Table 5, below, relates to the ATTACH result information element (IE). This IE in the ATTACH ACCEPT message indicates the result of the WTRU registration via the ATTACH REQUEST. Two new result values are added: EUTRAN/HSPA+ indicates the successful WTRU authentication and IP address allocation; the result of EUTRAN/HSPA+ +IMS indicates the successful WTRU authentication, IP address allocation and IMS Proxy location. TABLE 5 3GPP TS 24.008: Attach result information element Result of attach (octet 1) Bits 3 2 1 0 0 1 GPRS only attached 0 1 1 Combined GPRS/IMSI attached 0 1 0 EUTRAN (ATTACH + IP Address Allocation) 1 0 0 EUTRAN+IMS (ATTACH + IP Address Allocation + IMS Proxy) All other values are reserved. Follow-on proceed (octet 1) Bit 4 0 Follow-on proceed 1 No follow-on proceed Follow-on proceed is applicable only in lu mode. This indication shall be ignored if received in A/Gb mode.

The above method may be implemented in a WTRU acting in a wireless network, preferably a 3GPP LTE type network (OFDM) and by the 3G-UMTS-R7 (HSPA) network as well as an HSPA+ network, at the network layer, transport layer and application layer, as software or a system procedure. This invention applies to WCDMA, TDD, TD-SCDMA high chip rate, and FDD air interfaces and hence is air interface independent. 

1. A method for providing a single attachment operation of an internet multimedia system (IMS) enabled wireless transmit/receive unit (WTRU) to a wireless network, comprising: the WTRU: performing a registration of the WTRU with the network using an ATTACH procedure; and including an IMS session initiated protocol (SIP) registration request; and the network: upon completion of the attachment, providing to the WTRU authentication of the IMS, and enabling an IMS service subscribed by the WTRU via the SIP Registration.
 2. The method of claim 1, wherein the wireless network is a 3GPP long term evolution (LTE) network, the WTRU: sending registration to an enhanced UTRAN (EUTRAN), and an enhanced core (E-core) network.
 3. The method of claim 1, the WTRU: initially powering up; and activating IMS network services of the WTRU prior to initiating the ATTACH procedure.
 4. The method of claim 1, the network: allocating an IP address to the WTRU responsive to the ATTACH procedure.
 5. The method of claim 1, the WTRU, as part of ATTACH procedure: formatting an ATTACH request to the network to register the WTRU and its IMS service.
 6. The method of claim 5, the WTRU: including an Attach Type information element in the ATTACH request to substantially simultaneously attach the WTRU to the network, allocate an IP address and obtain an SIP registration.
 7. The method of claim 6, the WTRU: including an IMS SIP Registration information element (IE) as a part of the ATTACH request.
 8. The method of claim 7, the WTRU: encapsulating the IMS SIP Registration information element as an SIP Register message, to provide transparency of an upper layer service protocol message to current mobility management entities.
 9. The method of claim 8, the WTRU: including in the encapsulated SIP Register message an information element identifier (IEI) indicating that it is encapsulated, and a length indicator indicating a length of a value part of the information element, and the value part containing the entire SIP message.
 10. The method of claim 7, the WTRU: providing as the IMS SIP Registration information element a condensed message element that is of a minimum required length for SIP Registration.
 11. The method of claim 1, the network: sending an ATTACH ACCEPT information element that includes at least one of a private user identity and a public user identity for IMS authentication.
 12. The method of claim 11, the network: including as part of the ATTACH ACCEPT information element to the WTRU the allocated IP address and a chosen Proxy Call Session Control Function (P-CSCF) address responsive to the ATTACH REQUEST.
 13. The method of claim 11, the network: including as part of the ATTACH ACCEPT information element (IE) an EUTRAN/HSPA result indicator that indicates a successful WTRU authentication and IP address allocation.
 14. The method of claim 11, the network: including as part of the ATTACH ACCEPT information element an EUTRANHSPA+ +IMS indicator that indicates successful WTRU authentication, IP address allocation and IMS Proxy location.
 15. The method of claim 1, the network: providing SIP Registration private and public user identities for IMS authentication IMPI and IMPU which include one or more of the following information elements: Request-URI; From; To; Call-Id; Cseq; PrivateUserIdentity; PublicUserIdentity; and Expire.
 16. The method of claim 1, wherein the wireless network is a 3GPP Evolved HSPA FDD network, the WTRU: providing an attachment including registration to an enhanced UTRAN (E-EUTRAN), and an enhanced core (E-Core) network.
 17. A WTRU, comprising: an IMS configured to provide IMS services; an NAS configured to format an ATTACH request; and an RRC configured to provide a signaling link for the ATTACH request, whereby the ATTACH request includes an IMS registration component to obtain registration of the IMS service as part of the ATTACH procedure.
 18. The WTRU of claim 17, wherein the IMS registration component is an IMS Registration information element (IE).
 19. The WTRU of claim 18, wherein the IMS Registration IE is encapsulated.
 20. The WTRU of claim 19, wherein the encapsulated IMS Registration IE comprises an IE identifier (IEI) to indicate it is encapsulated.
 21. The WTRU of claim 20 wherein the encapsulated IMS Registration IE further comprises: a length indicator indicating a length of a value part of the information element (IE), and the value part containing the entire SIP message.
 22. The WTRU of claim 18, wherein the IMS Registration IE is a condensed message element that is of a minimum required length for SIP Registration.
 23. A network, comprising: a core having: first means configured to receive an ATTACH request from a WTRU through a UTRAN and perform WTRU authentication; second means configured to select a proxy call session control function (P-CSCF); and third means to register the WTRU and enable IMS service as part of an ATTACH procedure responsive to receipt of a request for IMS service from said WTRU, which request is part of the ATTACH request from the WTRU.
 24. The network of claim 23, wherein the request for IMS service comprises and information element (IE) which is part of the ATTACH request.
 25. The network of claim 24, wherein the IE comprises: an IE identifier (IEI); a length indicator indicating a length of a value part, followed by the value part.
 26. The network of claim 23, wherein the core further comprises: fourth means configured to provide an ATTACH accept message to the WTRU indicating successful UTRAN Attach and SIP registration.
 27. The network of claim 26, wherein the ATTACH accept message is comprised of three bits having given binary states.
 28. The network of claim 23, wherein the core as an enhanced core (E-core) and the UTRAN is an enhanced UTRAN (EUTRAN).
 29. The network of claim 23, wherein the core as an enhanced core (E-core) and the UTRAN is a 3GPP Long Term Evolution (LTE) enhanced UTRAN (EUTRAN).
 30. The network of claim 23, wherein the core as an enhanced core (E-core) and the UTRAN is a 3GPP Long Term Evolution (LTE) enhanced UTRAN (EUTRAN).
 31. A system comprising a network and at least one WTRU: said WTRU comprising: an IMS configured to provide IMS services; an NAS configured to format an ATTACH request; and an RRC configured to provide a signaling link for the ATTACH request, whereby the ATTACH request includes an IMS registration component to obtain registration of the IMS service as part of the ATTACH procedure; and said network comprising: a core comprising: first means configured to receive an ATTACH request from said WTRU through a UTRAN and perform WTRU authentication; second means configured to select a proxy call session control function (P-CSCF); and third means to register the WTRU and enable IMS service as part of an ATTACH procedure responsive to receipt of a request for IMS service from said WTRU, which request is part of the ATTACH request from the WTRU. 